1. Field of the Invention
The invention is related to abrasive flow machining and, more particularly, to an abrasive flow machining apparatus capable of processing an orifice within a part by carefully controlling the media flow rate. The invention is also directed to a method for such processing.
2. Description of the Related Art
Abrasive flow machining is the process of polishing or abrading a workpiece by passing a viscous media having abrasive particles therein under pressure over the workpiece or through an orifice extending through the workpiece.
Conventional abrasive flow machining processes are designed to maintain a constant media extrusion pressure which often results in significant changes in media temperature, flow rate and viscosity which adversely impacts the system capability to accurately predict abrasive flow machine (AFM) processing times and, consequently, overall process results.
As an example, the media temperature increases as the flow rate of the media increases through an orifice. When the orifice is subjected to media under a constant pressure, the flow rate of the media through the orifice increases as the orifice walls becomes smoother and the orifice diameter increases. As a result, not only does the media temperature increase, but such an increase is localized to the media that passes through the orifice at a higher flow rate. This produces both excessively high temperatures and a non-uniform temperature distribution throughout the media. High temperatures and variations in temperatures throughout the media prevent the media from working in a consistent and effective fashion. Therefore, an apparatus and method that may effectively utilize the media while at the same time maintain the temperature of the media within a relatively narrow temperature band is desired.
U.S. Pat. No. 3,634,973, which is assigned to the assignee of the present invention, discloses a reciprocal machining structure utilizing abrasive media but operating in a fashion which does not provide for direct control of the media flow rate through an orifice. While this apparatus is capable of affective abrasive flow machining, such machining would be of a higher quality and the media would last longer if the flow rate were controlled.